let arr = ['a','b','c','d','e','f']


Array.prototype.my_includes = function(x,y){
    if(typeof y!== 'number'||y==NaN){
        y=0
    }
    for(let i =y;i<this.length;i++){
        if(x==this[i]){
            return true
        }
    }
    return false
}
const res = arr.my_includes('b',4)
console.log(res);
